Fluorescence-based techniques are playing an increasingly important role in the study of biological systems. New fluorescent probes ranging from small organic fluorophores to nanoparticles, such as quantum dots (Qdots), and various forms of genetically encoded green fluorescent proteins (GFPs) have been developed. These fluorescent probes have made new measurements and advances possible but they have their limitations, such as low brightness, insufficient photostability, or toxicity concerns. As a result, there continues to be a need for probes that improve upon the existing fluorescent labels or at least complement them.
Polymer dots (chromophoric polymer dots) have been developed as a new class of fluorescent nanoparticles. Compared to organic dyes and fluorescent proteins, chromophoric polymer dots can possess orders of magnitude greater brightness and are more resistant to photobleaching. When comparing to quantum dots (Qdots), for example, chromophoric polymer dots can be an order of magnitude brighter. Moreover, the dimensions of chromophoric polymer dots can be tuned from several to tens of nanometers without affecting their spectral properties. Chromophoric polymer dots with small sizes are desirable in situations where labeling with large nanoparticles may perturb the native behavior of the tagged biomolecules. The small chromophoric polymer dots may also be useful in crowded cellular or intercellular spaces where they can better penetrate and distribute themselves. Various schemes have been developed to control the surface properties and bioconjugation of chromophoric polymer dots, which have provided use of chromophoric polymer dots for cell-surface and subcellular labeling. In addition, chromophoric polymer dot-based ratiometric sensors have been developed, including ones for pH, temperature, and ions, such as iron and copper.
Although chromophoric polymer dots represent a promising new class of fluorescent probes, there is a continued need to for developing methods and compositions involving the use of chromophoric polymer dots, e.g., methods and compositions for storing chromophoric polymer dots.